64bit + >3.6GB RAM = boom

[mmastrac]

Wow... I'm starting to get a little frustrated with the whole state of 64-bit computing. I'm not sure if the problem lies in the Linux kernel or ATI's drivers, but I'm guessing the latter. Of course, it could be that I've commented out that Save64BitBar code that was causing the driver to fail to load at all.

Has anyone managed to get a 64-bit Linux machine working with 4GB of RAM?

If I try to boot with >3.6GB enabled (mem=3600M, maxmem=3600M - not sure which of these options is used), I get a hard lockup when starting the X server now. My machine reports about 3.6GB in 32-bit as well.

I saw a similar problem with my SATA controller (it would advertise 64-bit DMA but could only handle 32-bit). I imagine that this could be a similar problem, but as ATI's drivers are just blobs I'm somewhat constrained in how much I can fiddle here.

I'm excited for the day when device manufacturers have access to 64-bit + >4GB machines! At least I can say that my experience under Linux was a little less painful than my brief Windows 64-bit experiments.

[yoshi314]

this could still be kernel-only related. i've seen many bugreports on lkml concerning machines with big amounts of ram.

[opera]

Has anyone managed to get a 64-bit Linux machine working with 4GB of RAM?

I run Debian unstable with my own custom-compiled kernel (2.6.20-rc1, because anything later crashes fglrx) in complete 64-bit mode, and I have 4 GB memory.

You need to use "AGP memory remapping" or something like that in the BIOS to access all the memory, and you need to NOT load the linux agp module (agp.ko). With that one loaded (static or as module), the kernel will oops.
If you're not sure how, just remove the agp.ko from the /lib/modules/[kernel]/[somewhere here].

Please reply for more details. I can give you my .config for instance.

[Alistair]

Keep in mind that the kernel folks have locked the AGP code into the kernel if you add IOMMU support to the kernels -- I think after 2.6.18 --

[opera]

Keep in mind that the kernel folks have locked the AGP code into the kernel if you add IOMMU support to the kernels -- I think after 2.6.18 --

I'm not certain atm how I do it, but I compiled intel-agp as a module, and the simply removed the .ko file from /lib/modules... Works for me.

[Alistair]

I'm not certain atm how I do it, but I compiled intel-agp as a module, and the simply removed the .ko file from /lib/modules... Works for me.

My comment was pointed at 64 bit kernels -

IF
on a 64 kernel you select IOMMU support -

this locks the AGP modules into the kernel. No module options.

IF you are in the 32 bit space or do not select IOMMU support you can make the agp code modules.

[Syzygies]

Intel D975XBX2 mobo, Core 2 Quad Q6600 Kentsfield, 4 GB ram works fine
with latest 64 bit Unbuntu 7.04.

This was my first build, I was too green to know there could be issues
like raised in this thread. The D975XBX2 was a conservative choice to
insure Linux compatibility. Fry's was carrying Intel's DQ35JO mobo
before it showed on Intel's site, and I very much wanted to build it
but could find nothing about compatibility. Given Fry's easy return
policy, I should have tried.

As a Mac expat, I love the money I saved and the control I gained, but
I find the stratification of the Linux community bizarre. One gets
cryptic, sometimes correct help on many forums, but one never sees
"Read the Linux Administration Manual and then ask for clarification."
This should be a tatoo. Then, why is compatibility an empirical
science? There should be a FAQ explaining how to make a mobo component
checklist, then how to read the Linux developer threads to check off
whether support for each component has been attempted. Only then
should "does it all work together?" become an empirical science.
Package managers should automate cataloging hardware configurations
that are alive enough to ask for updates; doing otherwise isn't
protecting privacy, it's protecting ignorance.

I'd say this 4 GB issue is a hardware compatibility issue. It would be
wider news if it worked for no one, and it worked with no special
effort for me.

[narf]

I have a ASUS A8N-SLI with dual-core Opteron, 4 Gb of RAM and nVidia 7600 GT. I had many problems until I got the latest BIOS upgrade and used the following kernel boot params:

mem=5G iommu=memaper noagp apicpmtimer acpi_use_timer_override notsc

Now it runs very well and I have 3803436k available RAM.

The machine will not boot at all without the mem=5G parameter.

Keep poking at the kernel params, sometimes the difference between horrible instability and smooth operation is a kernel parameter that doesn't seem to have anything to do with the symptoms.

[Kano]

Well 4 GB ram are not always working directly. But as long as your system is mainly for desktop use which would usually never need more than 2 GB ram then you can easyly go with 32 bit and "lose" 512 to 1024 MB and have no problem at all. 64 bit, especially with Debian/Ubuntu has more drawbacks than advantages. Mainly you can not easyly get a firefox/iceweasel browser with Java and Flash. Also every game needs usually 32 bit libs to run, of course there are ia32-libs and they would work, you still need some tricks to get wine running. As soon as you need a chroot for w32codecs then I would say don't use it at all... I am absolutely sure you will not find a desktop app that will run faster with 4 GB instead of 3 GB. Maybe try to find anything that runs faster with 3 GB than with 2... The 64 bit instruction set is faster for povray, oggenc and kernel compilation, but not for other apps with 32 bit asm optimasations - as you need C replacement code parts instead. The thing is different for servers when you need lots of ram for apache, mysql...

[Syzygies]

usually never need more than 2 GB ram

Is there an affordable mobo, 775 for Core 2 Quad, with 8 dimm slots?

Some of us use computers to compute. A gamer may care about speed, but as a mathematician I'd be happiest with a slow chip that could access 16 GB before it starts swapping. I'm already kicking myself for economizing by buying 4 GB of ram rather than 8 GB, even though I have 48 GB of swap spread over three non-OS drives.

64 bit Ubuntu works great for my needs.